Weak signal work with modes such as FT8, FT4, and JT65 all require software running on a computer with its time synchronized. The consequence of running a computer with its internal clock substantially out of sync is to neither be able to decode signals nor have your signals decoded by others.
You may have noticed hearing strong stations that were not decoding. It is likely that their computer’s clock was substantially out of sync with yours.
With the WSJT-X application, synchronization is measured by the DT value (time-differential). Small DT values are necessary for effective communication. If you happen to see an abundance of FT8 signals on the waterfall yet few decodes, or a distinct bias of negative DT values on decode, these are indicators that your computer’s clock is in need of synchronization.
Curious about your computer's clock synchronization? Use time.is to get a measurement of your computer's clock against a standard.
On Windows 10, it is fairly easy to manually sync the computer's clock. Though it is easy to forget to do this periodically which can lead to the computer's clock becoming unacceptably out-of-sync. Besides, computers are supposed to do this type of work for us humans anyway!
Fortunately, there is a handy little utility called NetTime that takes the work out of keeping your computer's clock synchronized within a milliseconds. NetTime is a Simple Network Time Protocol (SNTP) client which is easy to install and configure. The only real change I made to the default settings is setting the update interval to 15 minutes. 15 minutes happens to be the most frequent update value possible in the application.
Good DX and 73, NJ2X